DESIGN This is a prospective, observational cohort study with an intensive pharmacokinetic component conducted in HIV-negative healthy women. Genital tract and whole blood samples will be collected before, during, and after treatment with 7 days of oral MVC, dosed at 300mg twice daily (standard) or 300mg daily (reduced) compared with no treatment (control). Genital tract and plasma MVC concentration will be measured using intensive pharmacokinetic sampling to generate concentration-time profiles. Peripheral blood mononuclear cells (PBMC) and endocervical cells harvested from whole blood and cervicovaginal lavage respectively will be analyzed for CCR5 receptor occupancy, the number of CCR5-expressing HIV target cells, and level of T cell activation.